A gas chromatograph provides a gas chromatogram, which is prepared by introducing a subject gas to be detected together with a carrier gas into a gas separation column having a filling material therein, separating a gas component from the subject gas according to a deference in retention time caused by the interaction between the subject gas and the filling material in the gas separation column, and then detecting the separated gas component by a detector such as thermal conductivity detector (TCD) or flame ionization detector (FID).
At this time, since the retention time of the gas component in the gas separation column depends on temperature, the gas separation column is placed in a thermostatic chamber, and kept at an elevated temperature, so that the retention time of the gas component in the gas separation column can be maintained constant. As a result, accurate measurement becomes possible.
FIG. 14 is a schematic diagram showing this kind of gas chromatograph 6. A flow amount of a carrier gas supplied from a gas cylinder 7 through a gas flow channel 8 is controlled by a flow regulator 9. After the flow amount is detected by a flow sensor 10, a subject gas to be measured is supplied from a gas injection port 11, so that a mixture gas of the carrier gas and the subject gas is introduced into a gas separation column 1. The gas separation column 1 is placed in a thermostatic chamber 30, and kept constant at an elevated temperature. The gas provided from the gas separation column 1 is detected by a detector 14 to obtain the chromatogram.
The thermoplastic chamber 30 is composed of a heater 31, fan 32, and suction and discharge ports 33, 34, which have adjustable apertures. In the case of heating the gas separation column 1, the heater 31 is activated, and the fan 32 is rotated to send the air heated by the heater 31 to the gas separation column 1. The temperature of the gas separation column 1 is controlled by adjusting the apertures of the suction and discharge ports 33, 34 or a supply amount of electric power to the heater 31. In addition, when cooling the gas separation column 1, the suction and discharge ports 33, 34 are fully opened, and the fan 32 is rotated to circulate outside air through the thermostatic chamber 30.
By the way, in the gas chromatograph described above, the thermostatic chamber 30 must have a sufficient volume to stably keep the gas separation column 1 at the elevated temperature. Due to this reason, the device is easily large-sized as a whole. Particularly, in the medical field, it is being considered to introduce the gas chromatograph for a breath component analyzer for early detection of disease and monitoring of medical treatment effects, and the development of small-sized gas chromatograph is being expected.
In addition, according to the above device configuration, a pressurized carrier gas is sent from the gas cylinder 7 to the gas separation column 1. To downsize the device, it is suggested to use air as the carrier gas in place of the gas cylinder. However, there is a problem that the baseline of output of the detector 14 fluctuates due to the influence of miscellaneous gas mixed in the air, so that qualitative/quantitative analysis can not be achieved with reliability.